1. Field of the Invention
The present invention relates to a non-electrification polymeric composite material, more particularly to a non-electrification polymeric composite material capable of being suitably employed to hold a semiconductor substrate.
2. Description of the Prior Art
In producing a semiconductor device, there has been generally taken a series of such steps as etching a semiconductor wafer, washing the wafer, and the like, with the semiconductor wafer being held by a holder, or the like. Heretofore, as a material of this holder for holding the semiconductor wafer, has been used a chemically resistant and heat-resisting fluoro resin such as polytetrafluoroethylene (referred to as PTFE), a copolymer of perfluoro(alkyl vinyl ether) and tetrafluoroethylene (referred to as PFA), or the like. Each of such polytetrafluoroethylene (PTFE) and copolymer of perfluoro(alkyl vinyl ether) and tetrafluoroethylene (PFA) is excellent in electric insulation and has as high an electric resistivity as 10.sup.18 -10.sup.19 .OMEGA..cm at room temperature, and hence are apt to be readily electrified due to friction. Accordingly, in the case where the holder made of such fluoro resin material is dried by utilization of the centrifugal force and when rotated at a high speed, the holder is charged with static electricity due to friction between this holder and air. Consequently, the adjacent dust, dirt or the like is attracted to the thus electrified holder and then sticks to the surface of the semiconductor wafer, thereby resulting in decrease in yield of semiconductor chips.
One technique that overcomes the foregoing problem is described in Japanese Patent Application No. Tokukaisho 58-207651. This prior art discloses that mixing an electric conductor such as carbonaceous fiber, carbon black, or the like with a fluoro resin such as a copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) (PFA) produces a composite material which does not lose its chemical and heat resistance in respect to the fluoro resin contained therein and at the same time exhibits non-electrification characteristic per se. However, this prior art does not suggest, for example, any particular ratio of the carbonaceous fiber mixed with the copolymer of tetrafluoroethylene and perfluoro(alkyl vinyl ether) (PFA) to this copolymer. When, for example, carbon is added to the fluoro resin to make up a composite material, indiscreetly based on the disclosure of this prior art, the mechanical strength of the fluoro resin is affected by the so added carbon and further the melt viscosity of the resin is enhanced. In consequence, it becomes difficult to treat the composite material injection molding, owing to the higher melt viscosity thereof. In the etching process, furthermore, the carbon contained in the composite material is etched off into the etching solution, thereby presenting such a problem that the semiconductor wafer is soiled by the thus dropped carbon. Accordingly, the material merely deprived of its frictional electrification properties still does not sufficiently serve as the material of the holder employed for the production of the semiconductor device to hold the semiconductor wafer.